The present invention relates in general to lighting devices based on light-emitting diodes (LEDs) and in particular to tunable emitter modules that include multiple LEDs.
LEDs are a promising technology more energy efficient than incandescent light bulbs and are already widely deployed for specific purposes, such as traffic signals and flashlights. However, the development of LED-based lamps for general illumination has run into various difficulties. Among these is the difficulty of mass-producing lamps that provide a consistent color temperature.
As is known in the art, not all white light is the same. The quality of white light can be characterized by a color temperature, which ranges from the warm (slightly reddish or yellowish) glow of standard tungsten-filament light bulbs to the cool (bluish) starkness of fluorescent lights. Given existing processes for LED manufacture, mass-producing white LEDs with a consistent color temperature has proven to be a challenge.
Various solutions have been tried. For example, white LEDs can be binned according to color temperature and the LEDs for a particular lamp can be selected from the desired bin. However, the human eye is sensitive enough to color-temperature variation that a large number of bins is required, with the yield in any particular bin being relatively low. Another solution relies on mixing different colors of light to produce a desired temperature. However, this approach can be expensive and not reliable.
Therefore, there is a need for a multiple-LED emitter module that can be tuned to provide desired light colors.